The invention relates to establishing and certifying a torque output curve or classification for hydraulic hoists utilized in dump body applications. More particularly, the invention relates to methods and apparatus for determining or certifying whether a hydraulic hoist suitable for use in dump body applications meets a particular minimum body and payload torque requirement curve established in accordance with a mathematical formula presented herein.
A means of classifying hoists has previously been recommended and followed by member companies of the Hydraulic Hoist and Dump Body division of the Truck Body and Equipment Association, Inc. (TBEA) located in Washington, D.C. Reference is made to HYDRAULIC HOIST & DUMP BODY CLASSIFICATION CHART, Issue No. HH4DB774, published by TBEA in January of 1977. It is stated therein that:
The hoist rated net payload by class is based on the torque rating in inch pounds developed by the hoist around its hinge shaft, using an approximate weight of a standard type body, 12" overhand and a water level load. Hinge torque rating on a telescopic hoist will be established at the break-away position, and the hoist shall be capable of raising the rated load through the complete dumping angle.
It is believed that such a minimum torque rating is no longer valid as it does not accurately take into account the fact that the torque required to be exerted by a hoist to lift a given payload decreases as a function of the dump angle increasing. A formula has been derived to establish a new means of classifying hoists according to predetermined minimum body and payload torque requirement curve. In order to obtain a verification of the previous minimum torque rating of a particular hoist provided by an individual company, a relatively unsatisfactory trial and error method has heretofore been necessary.
More particularly, with a predetermined body size mounted upon the hoist to be tested, a load of, for example, steel stock or concrete blocks, with a known weight and center of gravity, was strapped to the body in an attempt to prevent it from moving during the dump cycle. The know weight was selected to correspond to the minimum torque rating of a given classification. If the hoist operated through its complete dump cycle, the hoist then met the minimum torque rating requirement for that classification. In addition to the troublesome requirement of obtaining the proper load, this method of certification proved difficult or unsatisfactory because of the load moving during the dump cycle.
In order to establish the exact minimum torque rating for the hoist, additional material had to be added in increments until such point that the hoist would not raise the load. With the known load, the exact minimum torque rating for the hoist could then be calculated. Under these test conditions, however, the particular angle in the dump angle cycle at which the hoist exerted a minimum torque was not necessarily known. Another serious disadvantage of the prior art procedure required to determine or varify the minimum torque rating of a hoist was the possibility of injury, should any component of the hoist fail during the dump cycle with the dump body heavily loaded.
This invention is concerned with this general area and has among its objects to provide a method and apparatus for use in certifying a torque output curve for a hoist which eliminates the above noted and other disadvantages of prior art certification of hoists.
More particularly, a mathematical formula is presented herein to establish a new means of classifying hoists in classes according to predetermined minimum body and payload torque requirement curves (MTR curves), and this invention has among its objects to provide a method and apparatus for use in determining or certifying whether a test hydraulic hoist utilized in dump body applications meets the MTR curve of a particular class.
Another of the principal objects of the invention is to provide such a method and apparatus for hoist certification which is not subject to the difficulties and the safety hazards involved in the prior art trial and error certification methods.
Another of the objects of the invention is to provide such a method and apparatus which will allow the torque which the hoist exerts at a particular dump angle to be determined.